1. Field of the Invention
The present invention relates to a recordable optical disk recording device. In particular, it relates to detection of a recording position shift, control of a recording operation, and control of a recording position during recording of information onto an optical disk having pre-pits, such as DVD-R/RW.
2. Background Art
Recently, various kinds of rewritable optical disk media, such as CD-R/RW, DVD-RAM, DVD-R/RW and DVD+R/RW, have appeared on the market.
Such optical disks already contain address information used as positional information for data recording, and user data is recorded on the disks using the address information.
For example, as for the DVD-R/RW, conventionally, there have been proposed an optical disk that has information recording tracks in guide grooves wobbling at a predetermined period and pre-pits formed at predetermined intervals on regions (lands) between the grooves, and a recording device that controls the rotation of the optical disk based on wobble signals detected from the grooves and controls the recording position based on pre-pit signals detected from the pre-pits (see Japanese Patent Laid-Open Publication No. 9-326138, for example).
The pre-pit is referred to also as land pre-pit because the pre-pit is formed on the land.
According to this conventional technique, even if the track pitch is narrow, accurate address information and disk rotation control information can be obtained.
Unlike DVD-RAM, according to this conventional technique, address information is not placed in the form of pits at the leading edges of sectors in the information recording track (in other words, no address pit exists in the groove forming the recording track). Therefore, high-density recording is possible, discontinuity of the recording information because of the address information is avoided, and the compatibility with read-only disks is high.
When recording user data on a DVD-R/RW, new data may be recorded following previously recorded data (incremental writing). In this case, according to the related standard, the precision of placement of the recorded data should fall within ±1 byte. If the precision is not achieved, the previously recorded data is overwritten and becomes unable to be read, and the reproduction stability is degraded because of the gap between the previously recorded data and the newly recorded data.
Thus, the user data to be recorded on the DVD-R/RW has to be always kept in an appropriate positional relationship with pre-pits. Therefore, means of detecting a recording position shift during recording or a process of stopping the recording or recovering the recording position to the original position based on the detection result is quite important.
In addition, there has been disclosed a technique of generating recording clock signals from a reproduced wobble signals so that variations of disk rotation can be followed when recording modulated data on an optical disk, such as DVD-R/RW (see Japanese Patent Laid-Open Publication No. 2001-357620, for example).
However, such an optical disk has a narrowed track pitch in order to perform high-density recording. As a result, a leakage from grooves adjacent to a track irradiated with a light beam, or a so-called crosstalk, cannot be ignored. If a crosstalk from an inner or outer adjacent groove occurs, the wobble signal interferes with the wobble signal component from the adjacent track, and the amplitude and phase thereof varies. In the case where the wobble signal is used for controlling the recording position, particularly if a phase of the wobble signal varies, the recording position cannot be controlled with a sufficient precision.
As for CD-R/RW or the like, conventionally, there has been used a method of recording data on the disk using clock signals of a fixed frequency generated by a quartz oscillator or the like. However, this method is not suitable for high-density disks, such as DVD-R/RW, because variations of disk rotation cannot be followed.
To the contrary, pre-pits are arranged so that the pre-pits do not interfere with each other, and therefore, the positions of the pre-pits on the optical disk can be accurately detected from the pre-pit signals detected from the pre-pits, and the recording position can be precisely controlled.
However, the format of pre-pits is complicated because of the relationship between EVEN frames and ODD frames, the presence of four kinds of bit patterns, and the like as described above. Furthermore, during recording, the pre-pit signals themselves may be unable to be stably reproduced because of high noise level. Therefore, it is quite difficult to generate a stable recording clock according to the condition of detection of the pre-pits.
There has been proposed a recording position controlling method using pre-pits (see Japanese Patent Laid-Open Publication No. 2004-95081, for example).
According to this conventional technique, in order that variations of disk rotation can be followed to some extent, a recording clock is generated based on wobbles, and recording is performed according to the recording clock. And in order to compensate for variations of wobble phase described above, the difference in phase between the address information generated by the modulating circuit and the pre-pit detection information is detected during recording, and the phase difference information is fed back to the recording clock. In this way, the correct recording position is stably maintained.
The phase difference detection according to the conventional technique described above is performed in the following two methods, for example.
A first method involves detecting the phase difference with a channel bit precision from the relationship between the modulated address information and the detected pre-pit position within one wobble and controlling the recording position to converge.
In this first method, a wobble signal may be missed due to a scratch or the like during recording, and the locked wobble output from the wobble PLL may slip in the lag or advance direction.
Typically, for example, in order to avoid the effect of such a scratch, the presence of the scratch is detected based on the envelope detection of wobble signals, and the PLL is held for the missed wobble signal based on the scratch detection result.
However, the capability of holding the PLL is limited to some extent, and particularly in the case of DVD-R/RW, the wobble is modulated in phase as described above. Therefore, the phase at the start of holding itself may be shifted from the center thereof, and a wobble slip is likely to result.
As described above, the recording clock is basically generated form the locked wobble, and therefore, if a wobble slip occurs, the recording position is shifted by one wobble.
According to the first method, if a recording position shift occurs due to such a wobble slip, the recording position control is performed with respect to the pre-pit at the position shifted by one wobble. Thus, the one-wobble-shifted state is maintained.
On the other hand, a second method involves detecting the phase difference between the sector SYNC position indicated by the modulated address information and the sector SYNC position detected by the pre-pit decoder with a byte precision in order to address the recording position shift exceeding ½ wobble that occurs when a wobble slip occurs, which is a problem with the first method.
According to this method, since the phase difference is detected based on the modulated address, the address for the pre-pit decoder, and the counter value for each sector, the effective control range is expanded to ±½ sector.
As a result, if a wobble slip described above occurs, the amount of the shift caused thereby is detected, so that the recording position control is performed, and the recording position is gradually recovered to the correct position during recording. In this example, the phase difference exceeding ±1 frame is clipped to prevent increase of the amount of information.
However, according to the second method, the address counter for pre-pit decoding has to operate normally. Thus, it is a prerequisite that the pre-pits can be precisely read during recording.
In order to achieve the prerequisite, synchronization conditions of synchronizing counters have to be stably assured. For example, as for sector synchronization, the SYNC patterns have to be continuously obtained.
In addition, the reliability of pre-pit decoding has to be high. Pre-pit data, which is composed of 8 bits for each sector (excluding the relative address), is added with a predetermined error correcting parity. Parity calculation is performed based on the obtained data, and if the calculation result is correct, it can be determined that the phase relationship among the synchronizing counters is correct.
However, during recording, the power of the laser light source varies according to whether to form a recording mark or not (that is, to form a space), so that the pre-pit signal amplitude also varies according to whether the laser forms a mark or a space. Furthermore, since the pre-pit signal is at a high frequency, it is difficult to distinguish the pre-pit signal from noise when the laser forms a space, and the pre-pit signal amplitude is low.
Therefore, it is difficult and impractical to stably and accurately detects a pre-pit.